Yeah,
I hate to admit it, though (despite my interest/tinkering over the years) I still have no clue what certain things mean. I know that 4:3 vs 16:9 is full vs widescreen but why is it that when even a professional movie studio releases a film fullscreen in 1080, it still needs to be pillarboxed? If they rescan the print, shouldn't they then be able to display it widescreen?!

IIWY, I'd stop using the term "fullscreen". A "widescreen" (aka 16:9) title plays FULL SCREEN on a 16:9 TV (which most are these days). A "fullscreen" (aka 4:3) image never plays as a FULL SCREEN on a 16:9 unless some doofus has set the display to stretch things out. Would make more sense to call it "narrow screen" or "square-ish screen".

Or better yet, call it 4:3 and 16:9. Then everyone knows what you're talking about.

As smrpix mentioned, a 4:3 image cannot be displayed correctlyANDfully on a 16:9 display (and vice-versa). It can either be displayed fully and incorrectly (stretching, and/or cropping) or correctly but not fully (letter/pillar-boxing).

Okay, but this had a wide theatrical release in '89. Why are the DVDs and even the iTunes version still in 1080 4:3? Yes, it's pillarboxed so it doesn't distort, but if rescanning why not just use the proper... eh, I don't think I even know what I'm trying to say or how to make it understood :/

Not sure but maybe do you mean the few theatrical wide screen typical widescreen 2.35 films that have been released as a cut down 4:3 version, sometimes seen on TV. But this would be a long long time ago. Sometimes a blockbuster is released on DVD that was shot as 2.35 is cropped to fill the 16:9 home TV frame rather than have black bars top and bottom, terrible practice but it does happen.

The IMDB reports it as "Aspect Ratio 1.85 : 1 "
You know how VLC lets you choose between fitting in the window or keeping the original resolution? The first shot is of the original resolution, the second if I make it fit the app's window.

Prior to the advent of HDTV virtually nothing was shot at 16:9. Common theatrical widescreen movie formats were wider than 16:9. The closest being 1.85:1, many at ~2:35:1. Since DVD and Blu-ray only support 4:3 and 16:9 DAR, any movie that doesn't have one of those aspect ratios will be cropped, pillarboxed or letterboxed.

Less popular movies are often mastered from old 4:3 studio video tapes. Hence they are pan-and-scanned to 4:3.

I don't know exactly what you're showing in those screen caps. In the last one, the image is very close to 16:9 after removing the black borders.

Do you realize that when viewing video in a full screen WINDOW on a 16:9 display, after leaving room for the Start bar, the window's borders, the title bar, the menu bar, and VLC's transport controls you don't have a 16:9 view port? You disproportionally lose space at the top and bottom of the screen so the view port is wider than 16:9.